January 21, 2022

Basic concepts of temperature meters and quick thermometers

A temperature meter is a physical quantity that characterizes how hot and cold an object is. Fast pyrometers can only be measured indirectly through certain characteristics of the object as a function of temperature, and the scale used to measure the value of an object's temperature is called a temperature scale. It specifies the starting point (zero point) for reading the temperature and the basic unit for measuring the temperature. At present, Shanghai Automation Instrumentation Co., Ltd.'s products use more standard temperature scales are Fahrenheit, Celsius temperature scale, thermodynamic temperature scale and the international practical temperature scale.

The Fahrenheit temperature scale (oF) stipulates: Under standard atmospheric pressure, the melting point of ice is 32 degrees, the boiling point of water is 212 degrees, and the middle is divided into 180 equal parts. Each is divided into 1 degree of newspaper and the symbol is oF.

Celsius temperature (°C) stipulates: Under standard atmospheric pressure, the melting point of ice is 0 degrees, the boiling point of water is 100 degrees, the middle is divided into 100 equal parts, each is divided into 1 degree of newspaper, the symbol is °C.

The thermodynamic temperature scale, also known as the Kelvin temperature scale, or absolute temperature scale, specifies that the temperature when the molecular motion is stopped is absolutely zero, and the symbol is K.

The international practical temperature scale is an internationally agreed temperature scale. It is close to the thermodynamic temperature scale, and it has high reproduction accuracy and is easy to use. At present, the international common temperature scale is the "International Practical Temperature Scale of 1968 - Revision of 1975" passed by the 15th International Conference on Weights in 1975, which is recorded as IPTS-68 (Rev-75). However, due to the lack of IPTS-68 temperature indication, the International Metrology Commission authorized the seventh resolution of the 18th International Metrological Conference to the 1989 Conference to adopt the 1990 international standard ITS-90, ITS-90 temperature scale instead of IPTS-68. Since January 1, 1994, China has fully implemented the ITS-90 international temperature scale.

The introduction of the International Temperature Scale (ITS-90) in 1990 is as follows.

1. Temperature unit The thermodynamic temperature (symbol T) is the basic amount of the master's physical quantity. Its unit is Kelvin (symbol K) and is defined as 1/273.16 of the thermodynamic temperature of the water triple point. Since the previous temperature scale definition uses a difference from 273.15K (freezing point) to represent the temperature, this method is still preserved.

By definition, the degree Celsius is equal to Kelvin, and the temperature difference can also be expressed in degrees Celsius or Kelvin.

The international temperature scale ITS-90 defines both the international Kelvin temperature (symbol T90) and the international Celsius temperature (symbol t90).

2. The general rule of the international temperature scale ITS-90 ITS-90 upwards from the 0.65K to Planck radiation law using the monochromatic radiation of the actual measurable maximum temperature. ITS-90 was developed in such a way that the T90 value at any temperature is very close to the best estimate of T at the temperature scale adoption in the full scale. Compared with the direct measurement of the thermodynamic temperature, the T90 measurement is much more convenient and more convenient. It is precise and highly reproducible.

3. The definition of ITS-90 is that the first temperature zone is between 0.65K and 5.00K, and T90 is defined by the relationship between vapor pressure and temperature of 3He and 4He.

The second temperature zone is 3.0K to the triple point (24.5661K). The T90 is defined by the helium gas thermometer.

The second temperature zone is between the equilibrium hydrogen triple point (13.8033K) and the silver solidification point (961.78°C). The T90 is defined by a platinum resistance thermometer. It uses a defined set of fixed points and utilizes the specified interpolation method. To index.

In the temperature zone above the freezing point of silver (961.78°C), T90 is defined according to Planck's radiation law, and the reproducing instrument is an optical pyrometer.

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